Rapid Hydrographic, Optical and Microstructure Surveys on the Continental Shelf and Slope

摘要

As part of the Coastal Mixing and Optics Accelerated Research Initiative, measurements of density, light absorption/attenuation and microstructure were made using sensors mounted on a towed undulating platform. The sensor suite included a conductivity-temperature-depth instrument, a nine- wavelength spectral absorption and attenuation meter, and a new microstructure instrument. Surveys were conducted during August 1996 and April-May 1997 in the Middle Atlantic Bight near 40.5N, 70.5W Time-dependent maps of the three- dimensional distributions of hydrographic, velocity and optical properties over the shelf and slope showed the importance of mesoscale and sub-mesoscale features. Evidence for secondary circulation associated with a shelfbreak front, an important process for frontal formation/maintenance and the vertical flux of nutrients, was obtained by jointly analyzing the hydrographic, optical and velocity data. Microscale conductivity fluctuations measured with a new high- frequency turbulence measuring instrument were used to determine temperature dissipation rate, the Cox number and the scaler diathermal turbulent diffusivity. Observed diffusivities near the shelfbreak front were two orders of magnitude larger than mid-ocean thermocline values. The multi-wavelength light absorption measurements were decomposed into contributions from the major absorbing components of seawater: phytoplankton, gelbstoff and tripton. The inherent optical property distributions were, to first-order, controlled by the physics.